It is known that optical radiation can be employed in non-contact systems which measure and/or verify the three-dimensional coordinates of specific points within a predetermined frame of reference. Such systems have a wide variety of beneficial applications, including use within the fields of metrology, robotics, quality control and machine/tool calibration. To date, two non-contact systems are known to have been employed for such purposes.
In a first system, a point light source is provided at a specific location, the three-dimensional coordinates of which are to be measured relative to a predetermined frame of reference. The optical radiation emitted from the point source is received by at least two light-sensitive array detectors (e.g. television cameras) that are positioned in such a manner that a triangle is defined by the point source and two detectors. Each detector senses the two-dimensional position of the point light source relative to the optical center axis of the detector, and such positional information is transmitted by electrical signals to a processor means. Knowledge of the precise orientation of each detector relative to the predetermined frame of reference, together with the information conveyed by the aforementioned electrical signals, allows the processor means to determine the three-dimensional coordinates of the point light source by triangulation methods. As may be appreciated, the above-described system requires substantial pre-calibration of both detectors relative to the predetermined frame of reference in order to ensure that the electrical signals transmitted by each detector can be accurately interrelated in carrying out the triangulation calculations. In addition, the two-detector system is substantially limited in actual practice to the measurement of the three-dimensional coordinates of one specific location at a time.
In a second known system, a coherent beam of light of a known wavelength is initially separated into first and second portions in a Michelson interferometer. The first portion of the separated beam is reflected internally within the interferometer, and the second portion of the beam is directed outward towards a cooperative surface, (e.g. mirror, Fresnel zone plate, etc.), which is centered about a specific point location, the three-dimensional coordinates of which are to be measured or verified relative to the Michelson interferometer. Upon reflection off of the cooperative surface, the second portion of the light beam is reunited with the first portion of the light beam on a common optical path within the Michelson interferometer to create circular interference fringes. By employing known fringe detection and counting techniques, one of the three-dimensional coordinates of the specific point location can be determined relative to the Michelson interferometer. Due to alignment requirements arising out of the manner of usage of the Michelson interferometer, the aforementioned circular interference fringes will not be created unless the aforementioned specific point lies on the known optical center axis of the Michelson interferometer. As such, it should be apparent that this system, in effect, is only capable of optically measuring one coordinate and optically verifying the other two coordinates for a specific point location. It should also be appreciated that the use of the above-described measuring system is limited to situations where a coherent light source and cooperative surface are present. Furthermore, the use of a Michelson interferometer in this system necessitates laborious two-dimensional pre-alignment procedures to ensure that interference fringes will be created.